Figure out what stair series and drive type you have. If it's a two step stair on a Class A, it's probably a series 32. Being an older stair (pre 2000) you may already have an updated controller/motor/gearbox (if someone previously upgraded it) if its original, you may not. I don't believe you can still buy new older series parts and you generally can't mix older generation parts with upgraded parts. You'll probably need to upgrade your controller and gearbox on your older series 32 stairs. There is an upgrade kit available. If your stairs are rusted/worn/bent and the gearbox/controller missing, it may be better to just buy a whole new stair assembly, install it and start fresh.
Google is your friend. Parts are available in all the popular locations. (Amazon, Ebay, online RV parts dealers) Get the parts and drawing diagrams and confirm which stairs you have before ordering anything. There are several different drive/gearbox/linkage assemblies.
Google: "Kwikee Stair Step Parts"
Chum lee